When constructing roads in slants in a mountain region, etc., earth moving work, such as cutting and filling-up, is first carried out to form a necessary foundation by using a construction machine, such as a hydraulic excavator and a bulldozer, and the face of slope is then formed around the foundation by using the hydraulic excavator, etc. to prevent breaking of the ground. This slope-face forming is highly accurate excavation and shaping work and requires skills. Particularly, if the earth is excessively excavated up to a position under a target excavation surface, compacting work must be carried out by using a dedicated machine, such as a compactor, to provide the strength substantially equal to that of the base ground because simple backfilling is not sufficient to provide the required strength. This results in a large reduction of working efficiency. For that reason, an operator carefully performs the work of forming the face of slope so that the earth is no excavated beyond the target excavation surface.
On the other hand, as means for teaching the target excavation surface to the operator, numerical values indicating excavation targets, e.g., numerical values regarding the gradient and depth of the slope of surface, are obtained from the result of surveying an original landform at that time, and stakes or plates with those numerical values put on them are set up in many representative positions (called stake setting-up work). While looking at the set-up stakes, the operator operates an operating mechanism of the hydraulic excavator so that the target face of slope is formed. When forming the face of slope in complicated terrains such as slants in a mountain region, a large number of stakes or plates must be set up as guides along the three-dimensional landform, and hence a lot of time is required to carry out surveying and setting-up of the stakes.
In view of the problem mentioned above, JP,A 2001-98585, for example, discloses a device for guiding a target excavation surface through the steps of comparing a three-dimensional position of a construction machine, such as a hydraulic excavator, and the direction of an operating mechanism thereof with a three-dimensional target landform, computing a three-dimensional intersect line between a plane defining a vertical cross-section extending in the same direction as the orientation of the operating mechanism and the three-dimensional target landform, and displaying the computed intersect line together with illustrations of a machine body and the operating mechanism on the same screen of a display unit installed within a cab.
Also, a 3D-MC GPS shovel manufactured by Topcon Corporation, for example, is equipped with a known device wherein triangular polygons representing three-dimensional landforms are displayed on a touch-panel display unit installed in a cab, and an operator teaches one of the displayed triangular polygons, which corresponds to a target excavation surface, by directly touching a display screen, thereby displaying the target excavation surface in a different color.